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package server
import (
"fmt"
"log"
"net"
"time"
"linum/internal/blocklist"
"linum/internal/cache"
"linum/internal/dns"
"linum/internal/resolver"
)
type Config struct {
Addr string
Upstream string
BlockFile string
}
type Server struct {
cfg Config
resolver *resolver.Forwarder
cache *cache.Cache
blocklist *blocklist.Blocklist
}
func New(cfg Config) (*Server, error) {
bl, err := blocklist.Load(cfg.BlockFile)
if err != nil {
return nil, fmt.Errorf("blocklist: %w", err)
}
return &Server{
cfg: cfg,
resolver: resolver.NewForwarder(cfg.Upstream),
cache: cache.New(),
blocklist: bl,
}, nil
}
func (s *Server) ListenAndServe() error {
addr, err := net.ResolveUDPAddr("udp", s.cfg.Addr)
if err != nil {
return fmt.Errorf("resolve addr: %w", err)
}
conn, err := net.ListenUDP("udp", addr)
if err != nil {
return fmt.Errorf("listen: %w", err)
}
defer conn.Close()
log.Printf("linum listening on %s, upstream %s", s.cfg.Addr, s.cfg.Upstream)
buf := make([]byte, 4096)
for {
n, remote, err := conn.ReadFromUDP(buf)
if err != nil {
log.Printf("read error: %v", err)
continue
}
go s.handle(conn, remote, buf[:n])
}
}
func (s *Server) handle(conn *net.UDPConn, remote *net.UDPAddr, data []byte) {
start := time.Now()
query, err := dns.Unpack(data)
if err != nil {
log.Printf("unpack from %s: %v", remote, err)
return
}
if len(query.Question) == 0 {
return
}
q := query.Question[0]
log.Printf("query %s %s from %s", qtypeName(q.Type), q.Name.String(), remote)
if s.blocklist != nil && s.blocklist.Blocked(q.Name.String()) {
s.reply(conn, remote, s.blockedResponse(query))
log.Printf("blocked %s (%v)", q.Name.String(), time.Since(start))
return
}
if cached, ok := s.cache.Get(q.Name, q.Type, q.Class); ok {
resp := *cached
resp.Header.ID = query.Header.ID
s.reply(conn, remote, &resp)
log.Printf("cache hit %s (%v)", q.Name.String(), time.Since(start))
return
}
resp, err := s.resolver.Resolve(query)
if err != nil {
log.Printf("resolve %s: %v", q.Name.String(), err)
s.reply(conn, remote, s.servfailResponse(query))
return
}
if resp.Header.Rcode() == dns.RcodeNoError || resp.Header.Rcode() == dns.RcodeNxDomain {
ttl := s.minTTL(resp)
s.cache.Set(q.Name, q.Type, q.Class, resp, ttl)
}
s.reply(conn, remote, resp)
log.Printf("resolved %s (%v)", q.Name.String(), time.Since(start))
}
func (s *Server) blockedResponse(query *dns.Msg) *dns.Msg {
resp := &dns.Msg{}
resp.Header.ID = query.Header.ID
resp.Header.SetQR(true)
resp.Header.SetRD(true)
resp.Header.SetRA(true)
resp.Header.SetRCode(dns.RcodeNxDomain)
resp.Question = query.Question
return resp
}
func (s *Server) servfailResponse(query *dns.Msg) *dns.Msg {
resp := &dns.Msg{}
resp.Header.ID = query.Header.ID
resp.Header.SetQR(true)
resp.Header.SetRCode(dns.RcodeServFail)
resp.Question = query.Question
return resp
}
func (s *Server) minTTL(resp *dns.Msg) uint32 {
min := uint32(300)
for _, rr := range resp.Answer {
if rr.TTL < min {
min = rr.TTL
}
}
return min
}
func (s *Server) reply(conn *net.UDPConn, remote *net.UDPAddr, msg *dns.Msg) {
wire, err := dns.Pack(msg)
if err != nil {
log.Printf("pack error: %v", err)
return
}
if _, err := conn.WriteToUDP(wire, remote); err != nil {
log.Printf("write error to %s: %v", remote, err)
}
}
func qtypeName(t uint16) string {
names := map[uint16]string{
dns.TypeA: "A", dns.TypeNS: "NS", dns.TypeCNAME: "CNAME",
dns.TypeSOA: "SOA", dns.TypePTR: "PTR", dns.TypeMX: "MX",
dns.TypeTXT: "TXT", dns.TypeAAAA: "AAAA",
}
if name, ok := names[t]; ok {
return name
}
return fmt.Sprintf("TYPE%d", t)
}
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